Transistor and capacitor structures for analog memory neural network

ABSTRACT

A method for manufacturing a semiconductor device includes forming a plurality of transistors on a semiconductor substrate. The formation of the plurality of transistors includes recessing channels of at least two transistors of the plurality of transistors. In the method, a stacked capacitor is formed on the semiconductor substrate, and the stacked capacitor is electrically connected in parallel to the at least two transistors of the plurality of transistors comprising the recessed channels and to an additional one of the plurality of transistors. The stacked capacitor, the at least two transistors and the additional one of the plurality of transistors form a memory cell of a plurality of memory cells of a memory device.

TECHNICAL FIELD

The field generally relates to semiconductor devices and methods ofmanufacturing same and, in particular, to a transistor and capacitorstructure for a memory cell.

BACKGROUND

Dynamic random-access memory (DRAM) devices utilize capacitors to storebits of data in an integrated circuit. In a conventional DRAM memorycell, a metal-oxide-semiconductor field-effect transistor (MOSFET)functions as a control switch and a capacitor stores chargescorresponding to data that is to be stored. A capacitor, for example,can be charged or discharged, representing two values of a bit,conventionally referred to as 0 and 1. Capacitance increases with thesurface area of the capacitor and high capacitance prevents loss ofstored data. The way to increase the charge-storing capacity of acapacitor is to increase the dielectric coefficient of the dielectricmaterial and reduce the thickness of the dielectric material, plusincreasing the surface area of the capacitor.

Planar type capacitors undesirably occupy a large area of asemiconductor substrate and are not suited for high or large-scaleintegration. Highly-integrated DRAM devices may employ stackedcapacitors, which occupy less area of the semiconductor substrate, whilealso allowing for increases in surface area and correspondingcapacitance of the capacitor.

Memory devices can be stacked in a three-dimensional (3D) configurationin a stackable cross-gridded data access array, referred to as acrossbar array. Crossbar configurations have been applied to devicesimplementing neural networks.

There is a need for memory devices and structures utilizing stackedcapacitors in connection with a crossbar neural network.

SUMMARY

According to an exemplary embodiment of the present invention, a methodfor manufacturing a semiconductor device includes forming a plurality oftransistors on a semiconductor substrate. The formation of the pluralityof transistors includes recessing channels of at least two transistorsof the plurality of transistors. In the method, a stacked capacitor isformed on the semiconductor substrate, and the stacked capacitor iselectrically connected in parallel to the at least two transistors ofthe plurality of transistors comprising the recessed channels and to anadditional one of the plurality of transistors. The stacked capacitor,the at least two transistors and the additional one of the plurality oftransistors form a memory cell of a plurality of memory cells of amemory device.

According to an exemplary embodiment of the present invention, asemiconductor device includes a plurality of memory cells. Each memorycell includes first and second transistors each comprising a recessedchannel disposed on a semiconductor substrate, and a third transistordisposed on the semiconductor substrate. A stacked capacitor is alsodisposed on the semiconductor substrate. The stacked capacitor iselectrically connected in parallel to the first, second and thirdtransistors, where the transistors include at least one NFET and atleast one PFET.

According to an exemplary embodiment of the present invention, a methodfor manufacturing a semiconductor device includes forming first, secondand third transistors on a semiconductor substrate. The first, secondand third transistors respectively include first, second and thirdchannels. In the method, the first and second channels of the first andsecond transistors are recessed, and a stacked capacitor is formed onthe semiconductor substrate. The stacked capacitor is electricallyconnected in parallel to the first, second and third transistors. Thefirst, second and third transistors and the stacked capacitor form amemory cell of a plurality of memory cells of a memory device.

These and other exemplary embodiments of the invention will be describedin or become apparent from the following detailed description ofexemplary embodiments, which is to be read in connection with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the present invention will be described belowin more detail, with reference to the accompanying drawings, of which:

FIG. 1A is a circuit diagram illustrating a memory cell, according to anexemplary embodiment of the present invention.

FIG. 1B is a block diagram illustrating an array of memory cells,according to an exemplary embodiment of the present invention.

FIG. 2A is a cross-sectional view taken along the line A in FIG. 2Dillustrating channel recessing in a method of manufacturing asemiconductor device, according to an exemplary embodiment of thepresent invention.

FIG. 2B is a cross-sectional view taken along the line B in FIG. 2Dillustrating channel recessing in a method of manufacturing asemiconductor device, according to an exemplary embodiment of thepresent invention.

FIG. 2C is a cross-sectional view taken along the line C in FIG. 2Dillustrating channel recessing in a method of manufacturing asemiconductor device, according to an exemplary embodiment of thepresent invention.

FIG. 2D is a top down view illustrating channel recessing in a method ofmanufacturing a semiconductor device, according to an exemplaryembodiment of the present invention.

FIG. 3A is a cross-sectional view illustrating gate structure andhardmask formation in a method of manufacturing a semiconductor device,according to an exemplary embodiment of the present invention.

FIG. 3B is a cross-sectional view illustrating gate structure andhardmask formation in a method of manufacturing a semiconductor device,according to an exemplary embodiment of the present invention.

FIG. 4A is a cross-sectional view illustrating metallization in a methodof manufacturing a semiconductor device, according to an exemplaryembodiment of the present invention.

FIG. 4B is a cross-sectional view illustrating metallization in a methodof manufacturing a semiconductor device, according to an exemplaryembodiment of the present invention.

FIG. 5A is a top down view illustrating sacrificial layer deposition ina method of manufacturing a semiconductor device, according to anexemplary embodiment of the present invention.

FIG. 5B is a cross-sectional view taken along the line D in FIG. 5Aillustrating sacrificial layer deposition in a method of manufacturing asemiconductor device, according to an exemplary embodiment of thepresent invention.

FIG. 6 is a cross-sectional view illustrating capacitor bottom electrodeformation in a method of manufacturing a semiconductor device, accordingto an exemplary embodiment of the present invention.

FIG. 7 is a cross-sectional view illustrating dielectric spacerformation in a method of manufacturing a semiconductor device, accordingto an exemplary embodiment of the present invention.

FIG. 8 is a cross-sectional view illustrating sacrificial layer removalin a method of manufacturing a semiconductor device, according to anexemplary embodiment of the present invention.

FIG. 9 is a cross-sectional view illustrating capacitor dielectric andtop electrode formation in a method of manufacturing a semiconductordevice, according to an exemplary embodiment of the present invention.

FIG. 10 is a cross-sectional view illustrating capacitor top electrodeand underlying dielectric patterning in a method of manufacturing asemiconductor device, according to an exemplary embodiment of thepresent invention.

FIG. 11 is a cross-sectional view illustrating dielectric layerdeposition and planarization in a method of manufacturing asemiconductor device, according to an exemplary embodiment of thepresent invention.

FIG. 12A is a top down view illustrating contact formation in a methodof manufacturing a semiconductor device, according to an exemplaryembodiment of the present invention.

FIG. 12B is a cross-sectional view taken along the line D in FIG. 12Aillustrating contact formation in a method of manufacturing asemiconductor device, according to an exemplary embodiment of thepresent invention.

DETAILED DESCRIPTION

Exemplary embodiments of the invention will now be discussed in furtherdetail with regard to semiconductor devices and methods of manufacturingsame and, in particular, to NFET and PFET transistors having recessedand non-recessed channels, and connected in parallel to a stackedcapacitor in a memory cell of an array.

It is to be understood that the various layers and/or regions shown inthe accompanying drawings are not drawn to scale, and that one or morelayers and/or regions of a type commonly used in, for example,random-access memory (RAM), dynamic random-access memory (DRAM),field-effect transistor (FET), metal-oxide-semiconductor field-effecttransistor (MOSFET), fin field-effect transistor (FinFET), verticalfield-effect transistor (VFET), complementary metal oxide semiconductor(CMOS), nanowire FET, nanosheet FET, single electron transistor (SET)and/or other semiconductor devices may not be explicitly shown in agiven drawing. This does not imply that the layers and/or regions notexplicitly shown are omitted from the actual devices. In addition,certain elements may be left out of particular views for the sake ofclarity and/or simplicity when explanations are not necessarily focusedon the omitted elements. Moreover, the same or similar reference numbersused throughout the drawings are used to denote the same or similarfeatures, elements, or structures, and thus, a detailed explanation ofthe same or similar features, elements, or structures will notnecessarily be repeated for each of the drawings.

The semiconductor devices and methods for forming same in accordancewith embodiments of the present invention can be employed inapplications, hardware, and/or electronic systems. Suitable hardware andsystems for implementing embodiments of the invention may include, butare not limited to, personal computers, communication networks,electronic commerce systems, portable communications devices (e.g., celland smart phones), solid-state media storage devices, functionalcircuitry, etc. Systems and hardware incorporating the semiconductordevices are contemplated embodiments of the invention. Given theteachings of embodiments of the invention provided herein, one ofordinary skill in the art will be able to contemplate otherimplementations and applications of embodiments of the invention.

The embodiments of the present invention can be used in connection withsemiconductor devices that may require, RAMs, DRAMs, FETs, MOSFETs,FinFETs, VFETs, CMOSs, nanowire FETs, nanosheet FETs, and/or SETs. Byway of non-limiting example, the semiconductor devices can include, butare not necessarily limited to RAM, DRAM, FET, MOSFET, FinFET, VFET,CMOS, nanowire FET, nanosheet FET, and/or SET devices, and/orsemiconductor devices that use RAM, DRAM, FET, MOSFET, FinFET, VFET,CMOS, nanowire FET, nanosheet FET, and/or SET technology.

As used herein, “height” refers to a vertical size of an element (e.g.,a layer, trench, hole, opening, etc.) in the cross-sectional viewsmeasured from a bottom surface to a top surface of the element, and/ormeasured with respect to a surface on which the element is located.Conversely, a “depth” refers to a vertical size of an element (e.g., alayer, trench, hole, opening, etc.) in the cross-sectional viewsmeasured from a top surface to a bottom surface of the element. Termssuch as “thick”, “thickness”, “thin” or derivatives thereof may be usedin place of “height” where indicated.

As used herein, “lateral,” “lateral side,” “lateral surface” refers to aside surface of an element (e.g., a layer, opening, etc.), such as aleft or right side surface in the drawings.

As used herein, “width” or “length” refers to a size of an element(e.g., a layer, trench, hole, opening, etc.) in the drawings measuredfrom a side surface to an opposite surface of the element. Terms such as“thick”, “thickness”, “thin” or derivatives thereof may be used in placeof “width” or “length” where indicated.

As used herein, terms such as “upper”, “lower”, “right”, “left”,“vertical”, “horizontal”, “top”, “bottom”, and derivatives thereof shallrelate to the disclosed structures and methods, as oriented in thedrawing figures. For example, as used herein, “vertical” refers to adirection perpendicular to the top surface of the substrate in thecross-sectional views, and “horizontal” refers to a direction parallelto the top surface of the substrate in the cross-sectional views.

As used herein, unless otherwise specified, terms such as “on”,“overlying”, “atop”, “on top”, “positioned on” or “positioned atop” meanthat a first element is present on a second element, wherein interveningelements may be present between the first element and the secondelement. As used herein, unless otherwise specified, the term “directly”used in connection with the terms “on”, “overlying”, “atop”, “on top”,“positioned on” or “positioned atop” or the term “direct contact” meanthat a first element and a second element are connected without anyintervening elements, such as, for example, intermediary conducting,insulating or semiconductor layers, present between the first elementand the second element.

In accordance with embodiments of the present invention stackedcapacitors are used to store analog information for a crossbar neuralnetwork. A memory device has a compact layout of a memory cell includinga parallel connected stacked capacitor utilized as a storage element, aread out transistor, and respective transistors providing currentsources for charging and discharging the memory cell. In order toachieve low current leakage from the capacitor, the two transistors forboth current sources have recessed channels resulting in longer gatelengths and the read out transistor also have a recessed channel.Alternatively, the read out transistor does not include a recessedchannel.

According to an embodiment of the present invention, a stacked DRAMcapacitor is built on top of three or more FETs, where the FETs includerecessed channels and non-recessed channels. The FETs are n-type andp-type FETs (NFETs and PFETs), and the stacked capacitor is connected inparallel to the transistors.

FIG. 1A is a circuit diagram illustrating a memory cell, and FIG. 1B isa block diagram illustrating an array of memory cells, according to anexemplary embodiment of the present invention. Referring to FIG. 1A, amemory cell 10 includes a parallel connected stacked capacitor 18utilized as a storage element, a read out transistor 16, and respectivetransistors 12 and 14 providing current sources for charging anddischarging the memory cell. In order to achieve low current leakage,the two transistors 12 and 14 for both current sources have recessedchannels and the read out transistor 16 does not have a recessedchannel. The charging transistor 12 is connected to a first gate voltageV1 and the discharging transistor 14 is connected to a second gatevoltage V2. Other logic peripheral circuits generate the appropriatelevel and duration of voltage for V1 and V2 to control the amount ofcharge and discharge.

Referring to FIG. 1B, an array 20 of memory cells 10 is formed, forexample, in a crossbar configuration for a neural network. The array 20includes wordlines 25 in the horizontal direction corresponding tovoltages V_(WL1), V_(WL2), V_(WL3) and V_(WL4), and bitlines 27 in thevertical direction corresponding to currents I1, I2, I3 and I4. Eachmemory cell 10 produces a controllable impedance w (e.g., w11, w12, w13and w14) which is controlled by the outputs of charging and dischargingtransistors 12 and 14. Source/drain outputs of readout transistor 16 arelabeled A and B in FIGS. 1A and 1B. A current (I) of a bitline is thesum of the respective products of a wordline voltage of each memory cell10 and a corresponding controllable impedance produced by the memorycell 10. For example, the currentI₁=V_(WL1)*w11+V_(WL2)*w12+V_(WL3)*w13+V_(WL4)*w14.

FIGS. 2A, 2B and 2C are cross-sectional views taken along the lines A, Band C, respectively of the top view in FIG. 2D illustrating channelrecessing in a method of manufacturing a semiconductor device, accordingto an exemplary embodiment of the present invention. Referring to FIGS.2A-2D, a semiconductor substrate 102 includes semiconductor materialincluding, but not limited to, silicon (Si), silicon germanium (SiGe),silicon carbide (SiC), Si:C (carbon doped silicon), silicon germaniumcarbide (SiGeC), carbon doped silicon germanium (SiGe:C), II-V compoundsemiconductor or other like semiconductor. In addition, multiple layersof the semiconductor materials can be used as the semiconductor materialof the substrate. The semiconductor substrate 102 can be a bulksubstrate.

Trenches are formed in the substrate 102, by for example, a wet or dryetch process to form isolation regions, such as shallow trench isolation(STI) regions. A dielectric material layer 104 including, but notnecessarily limited to silicon oxide (SiOx), where x is, for example, 2in the case of silicon dioxide (SiO₂), or 1.99 or 2.01, low-temperatureoxide (LTO), high-temperature oxide (HTO), flowable oxide (FOX), siliconoxycarbide (SiOC), silicon oxycarbonitride (SiOCN) or some otherdielectric, is formed in the trenches to define the isolation regions.

Four transistor well regions 106 and 108 are formed, including 2 PFETtransistor well regions 106, and two NFET transistor well regions 108.Three of the four resulting transistors may be used for a memory cell 10(e.g., 2 PFETs and one NFET). Alternatively, 2 NFETs and one PFET can beused. A remaining one of the four resulting transistors can be used forother circuits. While four transistor well regions 106 and 108 aredescribed, it is to be understood that the embodiments of the presentinvention are not limited thereto, and more than four transistors can beused on the substrate 102. Although embodiments of the present inventionare described in connection with planar transistors, the embodiments ofthe present invention are not necessarily limited thereto, and may applyto other types of transistors, such as, for example, FinFETs andnanowire FETs.

N-type wells and p-type wells are respectively implanted for the PFETtransistor well regions 106 and the NFET transistor well regions 108.The wells are implanted using, for example, block masks covering theregions not being implanted. Dopants may include, for example, an n-typedopant selected from a group of phosphorus (P), arsenic (As) andantimony (Sb), and a p-type dopant selected from a group of boron (B),gallium (Ga), indium (In), and thallium (Tl) at various concentrations.

Dummy gate structures including a dummy gate layer (not shown becauseFIGS. 2A-2D illustrate structures after dummy gate layer removal)surrounded by spacer layers 110, are formed on the transistor wellregions 106 and 108 after well implantation. The material of the dummygate layers includes, but is not necessarily limited to, amorphoussilicon, and the material of the spacer layers 110 includes, but is notnecessarily limited to, silicon boron nitride (SiBN),siliconborocarbonitride (SiBCN), silicon oxycarbonitride (SiOCN), SiN orSiOx.

Source/drain regions 116 and 118 are formed on portions of thetransistor well regions 106 and 108. Prior to removal of the dummy gatelayers, p-type source/drain regions 116 are formed on exposed portionsof the PFET transistor well regions 106 on either side of the dummy gatestructures and n-type source/drain regions 118 are formed on exposedportions of the NFET transistor well regions 108 on either side of thedummy gate structures. The source/drain regions 116 and 118 are formedby, for example, dopant implantation or in-situ doping during epitaxialgrowth of the source/drain regions. As noted above, dopants may include,for example, an n-type dopant selected from a group of P, As andantimony Sb, and a p-type dopant selected from a group of B, Ga, In, andTl at various concentrations. For example, in a non-limiting example, adopant concentration range may be 1×10¹⁸/cm³ to 1×10²¹/cm³.

Terms such as “epitaxial growth and/or deposition” and “epitaxiallyformed and/or grown” refer to the growth of a semiconductor material ona deposition surface of a semiconductor material, in which thesemiconductor material being grown has the same crystallinecharacteristics as the semiconductor material of the deposition surface.In an epitaxial deposition process, the chemical reactants provided bythe source gases are controlled and the system parameters are set sothat the depositing atoms arrive at the deposition surface of thesemiconductor substrate with sufficient energy to move around on thesurface and orient themselves to the crystal arrangement of the atoms ofthe deposition surface. Therefore, an epitaxial semiconductor materialhas the same crystalline characteristics as the deposition surface onwhich it is formed. For example, an epitaxial semiconductor materialdeposited on a {100} crystal surface will take on a {100} orientation.In some embodiments, epitaxial growth and/or deposition processes areselective to forming on a semiconductor surface, and do not depositmaterial on dielectric surfaces, such as silicon dioxide or siliconnitride surfaces.

Examples of various epitaxial growth processes include, for example,rapid thermal chemical vapor deposition (RTCVD), low-energy plasmadeposition (LEPD), ultra-high vacuum chemical vapor deposition (UHVCVD),atmospheric pressure chemical vapor deposition (APCVD) and molecularbeam epitaxy (MBE). The temperature for an epitaxial deposition processcan range from 500° C. to 900° C. Although higher temperature typicallyresults in faster deposition, the faster deposition may result incrystal defects and film cracking.

A number of different sources may be used for the epitaxial growth ofthe compressively strained layer. In some embodiments, a gas source forthe deposition of epitaxial semiconductor material includes a siliconcontaining gas source, a germanium containing gas source, or acombination thereof. For example, an epitaxial silicon layer may bedeposited from a silicon gas source including, but not necessarilylimited to, silane, disilane, ldisilane, trisilane, tetrasilane,hexachlorodisilane, tetrachlorosilane, dichlorosilane, trichlorosilane,and combinations thereof. An epitaxial germanium layer can be depositedfrom a germanium gas source including, but not necessarily limited to,germane, digermane, halogermane, dichlorogermane, trichlorogermane,tetrachlorogermane and combinations thereof. While an epitaxial silicongermanium alloy layer can be formed utilizing a combination of such gassources. Carrier gases like hydrogen, nitrogen, helium and argon can beused.

A dielectric layer 114 is deposited on the source/drain regions 116 and118, on exposed portions of the dielectric layer 104, and on and aroundthe dummy gate structures including the dummy gate layers and the spacerlayers 110. The dielectric layer 114 includes the same or similarmaterials as the dielectric layer 104, can be deposited using, forexample, deposition techniques including, but not limited to, chemicalvapor deposition (CVD), plasma enhanced CVD (PECVD), radio-frequency CVD(RFCVD), physical vapor deposition (PVD), atomic layer deposition (ALD),molecular layer deposition (MLD), molecular beam deposition (MBD),pulsed laser deposition (PLD), liquid source misted chemical deposition(LSMCD), and/or sputtering. Following deposition of the dielectric layer114, excess portions of the dielectric layer 114 are removed by aplanarization process, such as, for example, chemical mechanicalpolishing (CMP), which planarizes the dielectric layer 114 down to thespacer layers 110.

The dummy gate layers are removed to provide openings 122 (depth d1)between the spacers 110 exposing channel portions 106′ and 108′ betweenthe source/drain regions 116, 118. A gate structure will be formed inthe openings 122. The dummy gate layers can be removed using a selectiveetch process that selectively removes the dummy gate layers with respectto the dielectric layer 114 and spacers 110. The etch can be, forexample, an isotropic etch, such as a wet chemical etch, or ananisotropic etch, such as reactive ion etching (RIE), ion beam etching,plasma etching or laser ablation. Prior to removal of the dummy gatelayers, top portions of the spacer layers 110 are removed to expose thedummy gate layers.

After removal of the dummy gate layers to form the openings 122, some ofthe exposed channel portions 106′ and 108′ are recessed to result indeeper openings 125 (depth d2) than the openings 122 in which the gatestructures will be formed. The deeper openings 125 will result intransistors having longer gate lengths, which results in less currentleakage from a corresponding capacitor in a memory cell. As can be seenin FIGS. 2B and 2C, upper surfaces of the recessed channel regions 106′or 108′ are recessed to heights below lower surfaces of the source/drainregions 116 and 118, whereas the non-recessed channel region 108′ has anupper surface which is coplanar or substantially coplanar with the uppersurface of the source/drain regions 118.

As noted above, in accordance with an embodiment of the presentinvention, the two transistors for both charging and discharging currentsources have recessed channels, while the read out transistor does nothave a recessed channel. Referring to FIGS. 2B, 2C and 2D, the channelportions 106′ and 108′ are recessed for three of the four transistors.For example, as noted by the outline R, the channel portions 106′corresponding to the two PFET transistors, and a channel portion 108′corresponding to one of the NFET transistors are recessed, while achannel portion 108′ of a remaining one of the NFET transistors is notrecessed. Any combination of the channel portions may be recesseddepending on the design of a chip and locations of the transistors forboth charging and discharging current sources. Based on theconfiguration in FIG. 2D, the top 2 PFETs (recessed) and the lower leftNFET (also recessed) correspond to a memory cell, while the lower right(non-recessed) NFET is not used in the memory cell. However, theembodiments of the present invention are not necessarily limitedthereto. For example, in an embodiment one of the transistorscorresponding to a read-out transistor is not recessed.

Recessing of the channel portions 106′ and 108′ is performed using, forexample, chlorine, flourine, or bromine based ME, and the depth of therecessed portion is about 0.1 μm to about 0.3 μm, resulting in anoverall gate length for transistors with a recessed channel of about 0.2μm to about 0.6 μm, and an overall gate length for transistors without arecessed channel of about 0.02 μm to about 0.1 μm.

FIGS. 3A and 3B are cross-sectional views illustrating gate structureand hardmask formation in a method of manufacturing a semiconductordevice, according to an exemplary embodiment of the present invention.The cross-sectional views in FIGS. 3A and 3B are taken along lines of atop view (not shown) corresponding to FIGS. 3A and 3B, and correspondingin location to the lines C and B, respectively, of FIG. 2D.

Referring to FIGS. 3A and 3B, gate structures are formed in the openings122 and 125 left after removal of the dummy gate structures and therecessing of the selected channel portions. The gate structures areformed on the channel portions 106′ and 108′ of the transistors. Eachgate structure includes, for example, a high-K dielectric layer 132lining a bottom and lateral sides of the openings 122, 125. The high-Kdielectric layer 132 includes, but is not necessarily limited to,HfO_(x) (hafnium oxide (e.g., HfO₂)), ZrO₂ (zirconium dioxide), hafniumzirconium oxide, Al₂O₃ (aluminum oxide), and Ta₂O₅ (tantalum V oxide) orother electronic grade (EG) oxide. Examples of high-k materials alsoinclude, but are not limited to, metal oxides such as hafnium siliconoxynitride, lanthanum oxide, lanthanum aluminum oxide, zirconium oxide,zirconium silicon oxide, zirconium silicon oxynitride, tantalum oxide,titanium oxide, barium strontium titanium oxide, barium titanium oxide,strontium titanium oxide, yttrium oxide, aluminum oxide, lead scandiumtantalum oxide, and lead zinc niobate.

A gate metal layer 130 is formed in each of the openings 122, 125 on thehigh-k dielectric layer 132. In accordance with an embodiment of thepresent invention, the gate metal layer 130 includes a work functionmetal (WFM) comprising, for example, titanium nitride (TiN), tantalumnitride (TaN), ruthenium (Ru), titanium aluminum nitride (TiAlN),titanium aluminum carbon nitride (TiAlCN), titanium aluminum carbide(TiAlC), tantalum aluminum carbide (TaAlC), tantalum aluminum carbonnitride (TaAlCN) or lanthanum (La) doped TiN or TaN, and at least oneother metal layer deposited on the WFM layer. The other metal layer mayinclude, but is not necessarily limited to, a low resistance metal, suchas, for example, tungsten, cobalt, zirconium, tantalum, titanium,aluminum, ruthenium, copper, metal carbides, metal nitrides, transitionmetal aluminides, tantalum carbide, titanium carbide, tantalum magnesiumcarbide, or combinations thereof. The gate metal layer 130 laterfunctions as a gate electrode.

The gate metal and high-k dielectric layers 130, 132 can be depositedusing one or more deposition techniques including, but not limited to,CVD, PECVD, RFCVD, PVD, ALD, MBD, PLD, and/or LSMCD, sputtering, and/orplating, followed by deposition of a hardmask layer 140 on each of thegate structures including the gate metal and high-k dielectric layers130, 132. The material of the hardmask layers 140 can be the same orsimilar to the material of the spacers 110, and can be deposited by oneof the noted deposition techniques, followed by planarization down tothe dielectric layer 114, using, for example, CMP. The spacers 110 arelocated on the gate structure, each having an edge located on a verticalsidewall of the gate structure including the high-k dielectric layer132.

FIGS. 4A and 4B are cross-sectional views illustrating source/draincontact formation and metallization in a method of manufacturing asemiconductor device, according to an exemplary embodiment of thepresent invention. The cross-sectional views in FIGS. 4A and 4B aretaken along lines of a top view (not shown) corresponding to FIGS. 4Aand 4B, and corresponding in location to the lines C and B,respectively, of FIG. 2D.

Referring to FIGS. 4A and 4B, trenches are opened in the dielectriclayer 114 over the source/drain regions 116 and 118 using, for example,lithography followed by ME, to expose the source/drain regions 116 and118. Contacts to source/drain regions 116 and 118 are formed in thetrenches by filling the trenches with contact material layers 145-1,145-2, 145-3 and 145-4. Referring to FIG. 5A discussed further hereinbelow, additional source/drain contact layers 145-5, 145-6 and 145-7 canalso be formed to contact source/drain regions 118 of the NFETtransistors. The contact material layers 145-1, 145-2, 145-3, 145-4,145-5, 145-6 and 145-7 include, for example, electrically conductivematerial including, but not necessarily limited to, tungsten, cobalt,zirconium, tantalum, titanium, aluminum, ruthenium, and/or copper. Aliner layer including, for example, titanium and/or titanium nitride,may be formed on side and bottom surfaces of the trench and on thesource/drain regions 116 and 118 before filling the trench with thecontact material layers 145-1, 145-2, 145-3, 145-4, 145-5, 145-6 and145-7.

Deposition of the contact material layers 145-1, 145-2, 145-3, 145-4,145-5, 145-6 and 145-7 can be performed using one or more depositiontechniques, including, but not necessarily limited to, CVD, PECVD, PVD,ALD, MBD, PLD, LSMCD, and/or spin-on coating, followed by planarizationusing a planarization process, such as, for example, CMP.

Referring to FIGS. 4A and 4B (and to FIGS. 5A and 5B discussed furtherherein below), metallization, for example, back-end-of-line (BEOL)metallization is performed to form metal interconnects 150-1, 150-2,150-3, 150-4, 150-5, 150-6, 150-7, 150-8, 150-9 and 150-10 tosource/drain contacts and to gate metal layers 130. The number ofinterconnects and their patterns can vary based on design constraints.The metal interconnects 150-1, 150-2, 150-3, 150-4, 150-5, 150-6, 150-7,150-8, 150-9 and 150-10 include, for example, electrically conductivematerial including, but not necessarily limited to, tungsten, cobalt,zirconium, tantalum, titanium, aluminum, ruthenium, and/or copper, andcan be deposited using one or more of the deposition techniques notedherein.

Dielectric layers 155 and 160 are disposed on and around the metalinterconnects 150-1, 150-2, 150-3, 150-4, 150-5, 150-6, 150-7, 150-8,150-9 and 150-10. The dielectric layer 155 includes, for example,phosphosilicate glass (PSG), borosilicate glass (BSG), tetraethylorthosilicate (TEOS), an oxide or other similar dielectric, and thedielectric layer 160 includes, for example, a nitride, such as but notnecessarily limited to, SiBN, SiBCN, SiOCN or SiN. The dielectric layer160 is planarized using, for example, CMP.

FIG. 5A is a top down view and FIG. 5B is a cross-sectional view takenalong the line D in FIG. 5A illustrating sacrificial layer deposition ina method of manufacturing a semiconductor device, according to anexemplary embodiment of the present invention. Referring to FIGS. 5A-5B,sacrificial layers 165, 170 and 175 are deposited on the dielectriclayer 160 and on interconnect 150-2 using, for example, one or moredeposition techniques, including, but not necessarily limited to, CVD,PECVD, PVD, ALD, MBD, PLD, LSMCD, and/or spin-on coating, followed byplanarization using a planarization process, such as, for example, CMP.The sacrificial layers 165 and 175 include, for example, PSG,borosilicate glass BSG, TEOS, an oxide or other similar dielectric, andthe sacrificial layer 170 includes, for example, a nitride, such as butnot necessarily limited to, SiBN, SiBCN, SiOCN or SiN. In accordancewith an embodiment of the present invention, the sacrificial layer 170has an etch selectivity with respect to the sacrificial layers 165 and175, and the sacrificial layers 165 and 175 have an etch selectivitywith respect to the sacrificial layer 170. A combined thickness of thesacrificial layers 165, 170 and 175 is in the range of about 0.5 μm toabout 5 μm.

FIGS. 5B, 6-11 and 12B show a simplified diagram of device componentsunder the dielectric layer 155, where some elements have been omittedfrom the diagram for simplicity. In general, FIGS. 5B, 6-11 and 12Billustrate the PFET transistors corresponding to transistor well regions106 and interconnects 150-1 and 150-2 connected thereto. Thecross-sectional views in FIGS. 6-11 are taken along lines of top views(not shown) corresponding to FIGS. 6-11, respectively and correspondingin location to the line D of FIG. 5A.

FIG. 6 is a cross-sectional view illustrating stacked capacitor hole andcapacitor bottom electrode formation in a method of manufacturing asemiconductor device, according to an exemplary embodiment of thepresent invention. Referring to FIG. 6, a plurality of openings 180 areformed through the sacrificial layers 165, 170 and 175 where stackedcapacitors are going to be formed. The plurality of openings (or holes)180 are formed through the sacrificial layers 165, 170 and 175 exposingportions of the interconnect 150-2 and portions of dielectric layer 160.The openings 180 can be formed using, for example, fluorine based RIE.Although three openings 180 are shown, the embodiments of the presentinvention are not necessarily limited thereto, and more or less thanthree openings 180 for stacked capacitors can be formed.

Capacitor bottom electrodes 185 are deposited in the openings 180, andline bottom and lateral sides of the openings 180. In accordance with anembodiment of the present invention, the capacitor bottom electrodes 185include, but are not necessarily limited to, hemispherical grained (HSG)doped silicon, with a thickness from about 5 nm to about 50 nm. Thebottom electrodes 185 are deposited using, for example, one or moredeposition techniques, including, but not necessarily limited to CVD.

FIG. 7 is a cross-sectional view illustrating top sacrificial layerremoval and dielectric spacer formation in a method of manufacturing asemiconductor device, according to an exemplary embodiment of thepresent invention. Referring to FIG. 7, the top sacrificial layer 175 isselectively removed with respect to the bottom electrodes 185 down tothe middle sacrificial layer 170. The selective removal of the topsacrificial layer is performed using, for example, fluorine based RIE.

Then, dielectric spacers 190 are formed on exposed sides of the bottomelectrode 185 in and out of the openings 180. The dielectric spacers 190formed on exposed sides of the bottom electrode outside of the openings180 are formed on and cover portions of the middle sacrificial layer170. The dielectric spacers 190 are deposited using, for example, one ormore deposition techniques, including, but not necessarily limited to,CVD. Then, exposed portions of the middle sacrificial layer 170 (i.e.,not covered by the spacers 190) are selectively removed with respect tothe dielectric spacers 190, using, for example, fluorine based RIE. Thedielectric spacers 190 include the same or similar material as that ofthe bottom sacrificial layer 165.

FIG. 8 is a cross-sectional view illustrating sacrificial layer removalin a method of manufacturing a semiconductor device, according to anexemplary embodiment of the present invention. Referring to FIG. 8, thedielectric spacers 190 and the bottom sacrificial layer 165 areselectively removed with respect to the remaining portions of the middlesacrificial layer 170 and the bottom capacitor electrode 185. Theremaining portions of the middle sacrificial layer 170 providemechanical stability for the bottom capacitor electrodes 185 by bracingthe sides of the bottom capacitor electrodes 185 as shown in FIG. 8. Thedielectric spacers 190 and the bottom sacrificial layer 165 areselectively removed using, for example, HF wet etch.

FIG. 9 is a cross-sectional view illustrating capacitor dielectric andtop electrode formation in a method of manufacturing a semiconductordevice, according to an exemplary embodiment of the present invention.Referring to FIG. 9, capacitor dielectric layers 193 are conformallydeposited on the bottom electrodes 185 in and outside of the openings180, and on the exposed portions of the remaining middle sacrificiallayer 170, dielectric layer 160 and interconnect 150-2. The capacitordielectric layers 193 include, for example, a high-k material, such as,but not necessarily limited to, HfO_(x), ZrO₂, hafnium zirconium oxide,Al₂O₃, and Ta₂O₅ or other high-k dielectric material described herein.Top capacitor electrode layers 195 are conformally deposited on thecapacitor dielectric layers 193. The top capacitor electrode layers 195include, but are not necessarily limited to, TiN, TaN, W, etc. with athickness from about 5 nm to about 50 nm. The dielectric layers 193 andthe top electrode layers 195 are deposited using, for example, one ormore conformal deposition techniques, including, but not necessarilylimited to CVD or ALD.

FIG. 10 is a cross-sectional view illustrating capacitor top electrodeand underlying dielectric patterning in a method of manufacturing asemiconductor device, according to an exemplary embodiment of thepresent invention. Referring to FIG. 10, portions of the top capacitorelectrode 195 and portions of the capacitor dielectric 193 under theportions of the top capacitor electrode 195 are removed from regionswhere the top capacitor electrode and dielectric 195, 193 are notneeded. The removal of these portions of the top capacitor electrode anddielectric 195, 193 exposes portions of the dielectric layer 160 asshown in FIG. 10. The removal is performed using, for example, an etchprocess, and one or more masks to block removal of the remainingportions of the top capacitor electrode and dielectric 195, 193.

FIG. 11 is a cross-sectional view illustrating dielectric layerdeposition and planarization in a method of manufacturing asemiconductor device, according to an exemplary embodiment of thepresent invention. Referring to FIG. 11, a dielectric layer 205 isdeposited on the structure from FIG. 10, including on the exposedportions of the dielectric layer 160, and on and around the stackedcapacitors having the bottom and top electrodes 185 and 195, and thedielectric layer 193 between the bottom and top electrodes 185 and 195.The dielectric layer 205 includes the same or similar materials as thedielectric layers 104 and 114, can be deposited using, for example,deposition techniques including, but not limited to, CVD, PECVD, RFCVD,PVD, ALD, MLD, MBD, PLD, LSMCD, and/or sputtering. Following depositionof the dielectric layer 205, excess portions of the dielectric layer 205are removed by a planarization process, such as, for example, CMP.

FIG. 12A is a top down view and FIG. 12B is a cross-sectional view takenalong the line D in FIG. 12A illustrating contact formation in a methodof manufacturing a semiconductor device, according to an exemplaryembodiment of the present invention. Referring to FIGS. 12A-12B, contactholes are patterned in the dielectric layer 205 and filled with contactmaterial to form contacts 210-1, 210-2, 210-3, 210-4, 210-5, 210-6,210-7, 210-8, 210-9 and 210-10 to interconnects, capacitors,source/drain regions, and transistor gates. For example, the contactsshown in FIGS. 12A and 12B correspond to the circuit diagram in FIG. 1A,and carry gate voltages V₁ and V₂ and supply voltage V_(dd) fortransistors 12 and 14 providing current sources for charging anddischarging, provide connections to ground (GND) for the transistor 14and the capacitor 18, and source/drain outputs A and B of the readouttransistor 16. Referring to FIG. 12B, the contact 210-1 extends to theinterconnect 150-1 and to the gate metal 130 of the first PFETtransistor on the upper left in FIG. 12A, and the contact 210-2 isconnected to a capacitor 18 connected in parallel to the transistors 12,14 and 16. The number of contacts and their patterns can vary based ondesign constraints. The contacts 210-1, 210-2, 210-3, 210-4, 210-5,210-6, 210-7, 210-8, 210-9 and 210-10 include, for example, electricallyconductive material including, but not necessarily limited to, tungsten,cobalt, zirconium, tantalum, titanium, aluminum, ruthenium, and/orcopper, and can be deposited using one or more of the depositiontechniques noted herein.

Although illustrative embodiments of the present invention have beendescribed herein with reference to the accompanying drawings, it is tobe understood that the invention is not limited to those preciseembodiments, and that various other changes and modifications may bemade by one skilled in the art without departing from the scope orspirit of the invention.

We claim:
 1. A method for manufacturing a semiconductor device,comprising: forming a plurality of transistors on a semiconductorsubstrate, wherein forming the plurality of transistors comprisesrecessing channels of at least two transistors of the plurality oftransistors; forming a stacked capacitor on the semiconductor substrate;and electrically connecting the stacked capacitor in parallel to the atleast two transistors of the plurality of transistors comprising therecessed channels and to an additional one of the plurality oftransistors; wherein the stacked capacitor, the at least two transistorsand the additional one of the plurality of transistors form a memorycell of a plurality of memory cells of a memory device.
 2. The methodaccording to claim 1, wherein the at least two transistors of theplurality of transistors respectively provide current sources forcharging and discharging the memory cell.
 3. The method according toclaim 2, wherein the additional one of the plurality of transistorscomprises a read out transistor.
 4. The method according to claim 3,wherein the additional one of the plurality of transistors is without arecessed channel.
 5. The method according to claim 3, wherein theadditional one of the plurality of transistors comprises a shorter gatelength than the gate lengths of the at least two transistors of theplurality of transistors.
 6. The method according to claim 1, furthercomprising forming the plurality of memory cells in a crossbar array. 7.The method according to claim 1, wherein the recessing of the channelsof the at least two transistors of the plurality of transistorscomprises removing a portion of a channel region between source/drainregions for each of the at least two transistors.
 8. The methodaccording to claim 7, further comprising replacing the removed portionof the channel region with a gate structure in each of the at least twotransistors.
 9. The method according to claim 1, wherein forming thestacked capacitor on the semiconductor substrate comprises: forming aplurality of sacrificial layers on the semiconductor substrate, whereinthe plurality of sacrificial layers comprise a first sacrificial layer,a second sacrificial layer and a third sacrificial layer; forming anopening through the plurality of sacrificial layers; and depositing abottom capacitor electrode on bottom and lateral sides of the opening.10. The method according to claim 9, wherein forming the stackedcapacitor on the semiconductor substrate further comprises selectivelyremoving the third sacrificial layer with respect to the bottomcapacitor electrode and the second sacrificial layer.
 11. The methodaccording to claim 10, wherein forming the stacked capacitor on thesemiconductor substrate further comprises: forming a dielectric spacerlayer on side portions of the bottom electrode, and on portions of thesecond sacrificial layer; removing exposed portions of the secondsacrificial layer; and selectively removing the dielectric spacer layer.12. The method according to claim 11, wherein forming the stackedcapacitor on the semiconductor substrate further comprises selectivelyremoving the first sacrificial layer with respect to remaining portionsof the second sacrificial layer.
 13. The method according to claim 12,wherein forming the stacked capacitor on the semiconductor substratefurther comprises conformally depositing a top capacitor electrode and acapacitor dielectric layer on the bottom capacitor electrode and theremaining portions of the second sacrificial layer.
 14. The methodaccording to claim 1, wherein: a first transistor of the at least twotransistors is a p-type field effect transistor (PFET); a secondtransistor of the at least two transistors is an n-type field effecttransistor (NFET); and the stacked capacitor is connected to respectivesource/drain regions of the first and second transistors, and to a gateof the additional one of the plurality of transistors.
 15. Asemiconductor memory device, comprising: a plurality of memory cells,wherein each memory cell comprises: first and second transistors eachcomprising a recessed channel disposed on a semiconductor substrate; athird transistor disposed on the semiconductor substrate; and a stackedcapacitor disposed on the semiconductor substrate; wherein the stackedcapacitor is electrically connected in parallel to the first, second andthird transistors.
 16. The semiconductor memory device according toclaim 15, wherein: the first and second respectively provide currentsources for charging and discharging a memory cell; and the thirdtransistor comprises a read out transistor.
 17. The semiconductor memorydevice according to claim 16, wherein the third transistor is without arecessed channel, and comprises a shorter gate length than the gatelengths of the first and second transistors.
 18. The semiconductormemory device according to claim 15, wherein: the first transistor is ap-type field effect transistor (PFET); the second transistor is ann-type field effect transistor (NFET); and the stacked capacitor isconnected to respective source/drain regions of the first and secondtransistors, and to a gate of the third transistor.
 19. A method formanufacturing a semiconductor device, comprising: forming a firsttransistor comprising a first channel on a semiconductor substrate;forming a second transistor comprising a second channel on thesemiconductor substrate; forming a third transistor comprising a thirdchannel on the semiconductor substrate; recessing the first and secondchannels of the first and second transistors; forming a stackedcapacitor on the semiconductor substrate; and electrically connectingthe stacked capacitor in parallel to the first, second and thirdtransistors; wherein the first, second and third transistors and thestacked capacitor form a memory cell of a plurality of memory cells of amemory device.
 20. The method according to claim 19, wherein: the firsttransistor is a p-type field effect transistor (PFET); the secondtransistor is an n-type field effect transistor (NFET); and the stackedcapacitor is connected to respective source/drain regions of the firstand second transistors, and to a gate of the third transistor.